A day of reckoning for the surviving leaders of Cambodia's murderous Khmer Rouge regime came a step closer today with the swearing-in of Cambodian and foreign judges assigned to a special tribunal.

The 27 jurists were sworn in at a ceremony in the capital, Phnom Penh, from where residents were evacuated en masse in 1975 to toil in the "Killing Fields", which claimed an estimated 1.7 million lives through starvation, torture and overwork. The regime fell in 1979 after Vietnam invaded, triggering a civil war that petered out in the 1990s.

The ceremony marks an important step towards staging a trial that has been in preparation for almost a decade. Until now, none of the Khmer Rouge leaders has faced justice, and most live freely in Cambodia. Pol Pot, the secretive head of the movement, died in 1998.

Under a complex formula thrashed out between the prime minister, Hun Sen, and the United Nations, the three-year trial will focus only on senior Khmer Rouge leaders accused of crimes against humanity. All verdicts must be reached by a majority of the Cambodian and UN-selected judges based on international human rights law. Prosecutors will soon begin building cases against the suspects and trials are expected to begin by mid-2007.

Critics have accused Hun Sen, a former Khmer Rouge soldier who defected in 1977, of dragging his feet on the trials. Observers say the proceedings have the potential to embarrass China, which armed the Maoist regime and has in recent years emerged as Cambodia's biggest aid donor.

Most of the surviving Khmer Rouge leaders are in their 70s and 80s, and the protracted efforts to set up the tribunal at a military compound outside Phnom Penh could prove to be in vain if they die or are too ill to be tried.

Ta Mok, an army commander dubbed "the Butcher" for his readiness to kill comrades accused of disloyalty, is one of two Khmer Rouge suspects in detention. Last week, he was taken to hospital with high blood pressure and back pain, and could be too weak to stand trial.

However, Nuon Chea, "Brother Number Two" and second in the hierarchy to Pol Pot, said he was ready to face the tribunal. He told the Associated Press: "I will be glad to go, so that people in my country and other countries will know the truth of what happened. Whatever they ask, I will tell them."

Cambodians who survived the Killing Fields will be looking for more than a verdict on the regime's leaders. The tribunal is also being promoted as a way to set the record straight for the generation of Cambodians born after the genocide, who have little knowledge of the past.

Researchers into the regime's workings argue that without a full understanding of what drove the country to the brink of self-annihilation, Cambodia could repeat its past.